I. Field of the Invention
This invention relates generally to snowmobile-type recreational vehicles, and more particularly to an improved cooling system for such vehicles where the cooling capacity is directly proportional to engine power, allowing a more consistent engine temperature control under varying ambient conditions.
II. Discussion of the Prior Art
Various approaches are known in the art for cooling the internal combustion engine used to power snowmobile-type vehicles. In a first arrangement in the case of low horse power machines, the engine may be totally air-cooled by providing an appropriate opening in the engine cowl so that as the vehicle moves through the snow, air is rammed through the opening and made to flow across the exposed exterior surfaces of the engine. When idling or when travelling through deep snow, the ground speed of the vehicle may be such that insufficient air flows over the engine surfaces to provide adequate cooling and an over-temperature condition will frequency arise. This method is wholly unsuited for current machines due to sound level restrictions.
Another known cooling system is disclosed in U.S. Pat. No. 4,340,123 assigned to Kawasaki incorporates a liquid coolant heat exchanger which extends along the tunnel of the snowmobile at a location above the track assembly and below the seat. A combination of air flow and melting snow splashed onto the heat exchanger by the drive track carries the heat away from the recirculating coolant pumped through the coolant passages formed in the engine. Systems of this type which rely on a snow-splash cooled heat exchangers are dependent on outside conditions and not the cooling load and, therefore, do not maintain a constant temperature range under varying ambient conditions. For example, when traversing compacted snow or ice, very little snow is splashed by the drive track onto the heat exchanger and, accordingly, heat removal is achieved solely by the air which is made to pass over the heat exchanger. Again, if the vehicle is being driven at a slow speed for a prolonged time interval, say, over a frozen lake, over-heating can occur due to the inability of the heat exchanger to dissipate all of the heat generated by the engine. Moreover, systems such as disclosed in the aforereferenced Kawasaki patent often result in slush freezing on the tunnel surfaces and track suspension member, increasing the weight of the machine and adversely affecting performance. Moreover, with the heat exchanger disposed in the snowmobile's tunnel, the clearance between the drive track and the heat exchanger reduces the suspension stroke available, making it difficult to provide a comfortable ride.
The Fields et al. U.S. Pat. No. 4,249,626 also assigned to Kawasaki describes a snowmobile having a liquid-cooled engine with a radiator element positioned in front of a hood louver whereby air entering through the louvers as the machine is being driven passes through the radiator to extract the heat from the coolant liquid. Again, this type of design suffers from the fact that the amount of cooling provided is dependent to a large extent on ambient conditions, such as speed of travel, snow conditions, etc. and not to the power being generated by the vehicle's internal combustion engine. The amount of venting required to introduce the necessary cooling air also compounds the problem of snowmobile engine noise emissions and, accordingly, it is generally desirable to reduce, as much as possible, the area of openings in the vehicle's cowl or hood.
The prior art has also failed to adequately address a major heat source located beneath the vehicle's hood. More specifically, it is found that the engine's exhaust manifold, sometimes referred to as a "Y-pipe" in the case of a two cylinder engine, is a major source of under-the-hood heating Unless proper attention is paid to under-hood temperatures, such problems as vapor lock, heat bogging, and shortening of V-belt life occur.